In a semiconductor manufacturing process, a circuit pattern is formed through a series of processes of coating a photoresist film on a substrate such as a semiconductor wafer, exposing the photoresist film to light with a preset circuit pattern and developing the photoresist film. This process is called a photolithography process. In the photolithography process, a processing system in which an exposure apparatus is connected to a coating and developing apparatus is typically used.
In the photolithography process, a developing liquid is supplied on the substrate, and a soluble portion of the photoresist film is dissolved by this developing liquid, so that the required circuit pattern is formed. Thereafter, generally, a cleaning process is performed in order to remove the dissolved products and the developing liquid from a surface of the substrate.
Conventionally, a spin cleaning method is known for such a cleaning process. In this spin cleaning method, as shown in FIG. 28(a), a cleaning liquid L is supplied onto a central portion of a substrate (hereinafter, referred to as “wafer W”). Then, the wafer W is rotated about a vertical axis thereof, and a liquid film of the cleaning liquid L is formed by a centrifugal force. The dissolved products and the developing liquid are removed from the substrate by being washed away by a flow of the cleaning liquid L.
Further, as another cleaning method, there is known a substrate cleaning method and a substrate cleaning apparatus as illustrated in FIG. 29(a). In the substrate cleaning method and substrate cleaning apparatus, the wafer W is rotated about a vertical axis thereof while being held horizontally, and a cleaning liquid L is discharged to a central portion of the wafer W from a cleaning liquid nozzle 60 and diffused to the entire surface of the wafer W by the centrifugal force. Then, by discharging a gas G toward the central portion of the wafer W from a gas nozzle 70, a drying region is formed on the wafer W. Then, by moving the cleaning liquid nozzle 60 outward, the drying region is diffused to a peripheral portion of the wafer W. As a result, the wafer W is cleaned (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Laid-open Publication No. 2009-252855 (Claims)
In the conventional spin cleaning method, however, an effect of removing the dissolved products has been low, and it has taken a long time to complete a spin cleaning process. Further, recently, as for the wafer W on which minute circuit patterns P having a high aspect ratio are formed, dissolved products remaining between the circuit patterns P may not be cleaned sufficiently even if the conventional spin cleaning process is performed for a long time. That is, as for the wafer W having the circuit patterns P of the high aspect ratio, in the cleaning process after the developing process, the liquid film of the cleaning liquid L is moved on the wafer W toward the peripheral portion thereof by the centrifugal force generated by the rotation of the wafer W for a short time. Accordingly, the dissolved products between the circuit patterns may not be sufficiently removed by the cleaning liquid L. Further, if the supply of the cleaning liquid L is stopped, a stream of the cleaning liquid L may be cut at the peripheral portion of the wafer W where the centrifugal force is especially great, as illustrated in FIG. 28(b), so that the dissolved products and the cleaning liquid L may remain between the circuit patterns.
Moreover, even if the stream of the cleaning liquid L is prevented from being cut, the cleaning liquid L containing the dissolved products may remain between the circuit patterns, as depicted in FIG. 28(c).
As shown in FIG. 28(c), if surface tension of the cleaning liquid L between the circuit patterns becomes great, pattern damage may occur by the stress balance between the circuit patterns. Furthermore, if a rotation number of the wafer W is increased excessively, the circuit patterns may not stand against the stress generated by the rotation, resulting in the pattern damage. As a consequence, a development defect may be caused.
Meanwhile, it is described in Patent Document 1 that the cleaning liquid L is supplied to the central portion of the wafer W, and after forming the drying region by discharging the gas G to the central portion of the wafer W, the cleaning liquid nozzle 60 is moved at a speed lower than a speed at which the drying region is diffused outward, in order to prevent the stream of the cleaning liquid L from being cut. According to this substrate cleaning method, by moving the cleaning liquid nozzle 60 and the gas nozzle 70 from the central portion of the surface of the wafer W toward the peripheral portion thereof, the liquid film of the cleaning liquid L can be removed by the gas G discharged from the gas nozzle 70. Accordingly, the stream of the cleaning liquid L can be prevented from being cut. Even if the technique described in Patent Document 1 is used, however, it may be still difficult to remove the cleaning liquid L remaining between the circuit patterns having the high aspect ratio.
With the technique described in Patent Document 1, it may be possible to reduce a residual amount of the cleaning liquid L between the circuit patterns by decreasing the moving speed of the gas nozzle 70. After the gas nozzle 70 passes away, however, the centrifugal force would be applied to the circuit patterns P for a long time while the cleaning liquid L still remains between the circuit patterns P. As a result, the circuit patterns P may be damaged (see FIG. 29(b)).